Real-time system for detecting foreign bodies in food containers using ultrasound

ABSTRACT

An ultrasound system determines the presence of a foreign object in a container of fluid by measuring echo signals from the outer surface of the container and the inner surface of the container. The amplitude of the echo signals are compared to determine the presence of an object in the container. The system also determines viscosity of the contained fluid by measuring a through-transmission time through the container and the fluid, measuring an outer echo transmission time of an outer echo signal from the outer surface of the container and an inner echo transmission time of an inner echo signal from the inner surface of the container, and determining a time difference between the outer echo transmission time and the inner surface transmission time.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/263,383, filed Oct. 2, 2002 now U.S. Pat. No. 6,782,752, which claimspriority to U.S. Provisional Application Ser. No. 60/326,547, filed Oct.2, 2001.

FIELD OF THE INVENTION

The present invention relates to a container inspection system usingultrasonic technique for two objectives (1) on-line detect and inspectforeign objects in bottled beverages, and (2) on-line sort and classifythe bottled beverage based on their viscosity measurement.

BACKGROUND OF THE INVENTION

‘Foreign Objects’ (FOs) refers to any unwanted object in beverageproduct. Detection of FOs in beverages plays an important role insecurity control and quality assurance of food products. When beveragesare manufactured or packaged small foreign objects might end up in theproduct. Fragments of glass and metal scarf may be found in glass jarsor cans. It is naturally desirable for beverage production that all FOsare found and removed before they reach the consumers.

Mechanical separation techniques have been used for many years forfinding foreign objects in powdered and flowing products on the basis ofsize and weight. See e.g. A. J. Campbell, “Identification of ForeignBody Hazards and the Means for their Detection and Control,” (TechnicalBulletin No. 88, UK: Campden Food & Drink Research Association. 1992).This method is appropriate only before the beverage is packaged inbottles or containers. Optical techniques can be used for aftercontainer filling inspection, as described by T. Gomm and S. E. Price inU.S. Pat. No. 4,136,930 entitled “Method and apparatus for detectingforeign particles in full beverage containers” issued in 1979, and by P.Weathers in U.S. Pat. No. 2,427,319 entitled “Beverage inspectionmachine” issued in 1947, but they are limited to clear transparencybeverage bottles. X-rays and magnetic resonance imaging (MRI) could beanother options but they are expensive, safety uncertain and complicatedmethods. See e.g. B. Zhao, O. Basir and G. Mittal, “Prototype of ForeignBody Detector for Beverage Containers by Ultrasonic Technique,”submitted to Food research international in 2002, and B. Zhao, O. Basirand G. Mittal, “Foreign Body Detection in Foods by Ultrasound Pulse/echoMethod,” submitted to International Journal of Food Science & Technologyin 2001.

Low intensity ultrasonic techniques can be used in beverage inspectionbecause of their large applicability, reliability, safety and low cost.Nevertheless, there are only a limited number of publications related topackaged food inspections. For example, “Container inspectingapparatus,” described by K. Tadahisa, K. Kunihiko, M. Yasuo and N.Masaji in E.P. Pat. No. 0821230 issued in 1998, which uses ultrasonicvibration to agitate effervescence of beverage from the bottom of thecontainer to inspect the sealing performance.

The second publication is “Preliminary studies of a novel air—coupledultrasonic inspection system for food containers” presented by T. H.Gan., D. A. Hutchines, and D. R. Billson, Journal of Food Engineering,vol. 53, pp 315–323 (2002) in which FO suspended in low density materialcontainer (soft drink bottle) was tested using air coupled transducersin thru-transmission mode.

Air coupled ultrasonic techniques have two drawbacks. One is that itsapplication is limited to low density material due to the reflection ofmost of the transmitted energy because of acoustic impedance mismatch.The second is that this technique works in mode of separate transmitterand receiver. This mode is employed for either thru-transmission orsurface wave detection. Thru-transmission is not a good mode forinspecting FOs sediment at the bottle bottom because the ultrasoundsignal can not transmit from the transmitter to receiver when they areseparately placed under the bottom and above the top of the bottle beinginspected. This is due to the bottle neck which shields the ultrasoniclongitudinal transmission from bottom to cover. Surface wave techniquedetects flaws in a material by examining the time of flight of a pulsewith respect to that of a back wall echo (inner surface of the containerwall). This method is not suitable for detecting FOs inside a containersince the presence of FOs does not change the time of flight from theinner surface of the bottle wall.

Water coupling can be used in high density container materialsinspection. See. e.g. E. Haeggestrom, and M. Luukkala, “UltrasoundDetection and Identification of Foreign Bodies in Food Products”, FoodControl, vol. 12, p37 (2001), and M. Hiroshi, I. Sigeki, K. Tsukio, andN. Masanori in K.R. Pat. NO. 9,005,245, entitled “Inspection method andapparatus for wrapped contents by ultrasonic,” which is issued in 1990.However, in both of the publications the water tank immersion mode areused, which is not suitable for bottled beverage production on-lineinspection because of its low inspection speed. See e.g. Y. Jiang, B.Zhao, O. Basir and G. Mittal, “LabView Implementation of an UltrasoundSystem for Foreign Body Detection in Food Products,” submitted toComputers and Electronics in Agriculture in 2002.

In summary of the above-published ultrasonic techniques for foodinspection, a fatal drawback is that they use point-detection (using onetransducer or one pair of transducers). Only one small point of foodcontainer can be inspected each time by one transducer or transducerpair, which cannot catch up with the high speed food production. Theirmethods are therefore not suitable for on-line FOs inspection.

Product rating is another point for manufactures to optimize theirpricing and sale strategy. Viscosity is one of indices for productquality rating which can indicate the juice concentration, mouth feel,the ingredient functionality, and shelf life. Conventional liquidviscosity measurement is conducted by Couette, plate-and-conerotational, and parallel plate rheometers based on Poiseuille or Couetteflow or oscillating flow. A drawback of these conventional methods isthat they are normally conducted off-line. This makes it difficult tomonitor product quality in real-time. Especially, this off-lineinspection is an open-bottle percentage sampling method, i.e., onejudges the quality of a bench of production based on the examination ofone or two samples. The beverage quality in each individual closedbottle is different from each other but in fact is not known. Therefore,the quality of an individual bottle may be over-evaluated by the benchevaluation, which damages the reputation of the producer when it reachesconsumers. In the opposite case, the producer loses money if the qualityis under-evaluated by the bench evaluation.

Being rapid, non-destructive and non-invasive, ultrasonic technique is apromising approach for viscosity on-line measurement in food processingindustry. Using ultrasonic technique the viscosity measurement can beapproached by establishing a correlation between the viscosity ofbeverages and other measured physical properties of the ultrasoundsignal. R. Saggin, and J. N. Couplant described an ultrasonicreflectance coefficient method in “Ultrasonic characterization of oilviscosity and solids content” (2000 IFT Annual Meeting, Dallas, Tex.Jun. 11–14, 2000; 30D-11). An advantage of this method is that it onlyrequires the reflection signal at one interface. However, this techniqueemploys both amplitude and phase information at several frequencies todetermined the viscosity. This makes the viscosity computation processrelatively complicated. Furthermore, computing phase response in thespectrum is less accurate than that of computing amplitude response. M.J. McCarthy, R. L. Powell, J. A. Fort, D. M. Pfund, and D. M. Sheenpresented ultrasonic Doppler velocimetry for food viscosity measurement,“Development of ultrasonic Doppler velocimetry for viscositymeasurements” (2000 IFT Annual Meeting. Dallas, Tex. 2000 Jun. 11–14. nr49-6). They used ultrasonic Doppler Velocimetry to determine thevelocity profile in a tube. This technique needs not only an accuratevelocity measurement, but also an accurate spatial measurement andsubsequent data fitting for the profile. See e.g. B. Zhao, O. Basir andG. Mittal, “Correlation Analysis between Beverage Viscosity and SoundVelocity,” submitted to International Journal of Food Properties in2002.

Velocity measurement by pulse/echo method is the simplest, widely used,and probably the most accurate in ultrasonic techniques. Using velocityof sound as a measure of beverage viscosity requires a governing law topredict how the viscosity is correlated with the ultrasound velocity.However, there is no direct or explicit correlation between theviscosity and the velocity of sound. Furthermore, using time-of-flightmeasurement to correlate the fluid viscosity is normally performed in aconduit of volume flow, as described by M. Guitis in D.E. Pat. No.19940192, entitled “Device for determination of fluid parameters andfluid composition control based on on-line measurement of such fluidparameters using twin ultrasonic transducer and reflector arrays foraccurate measurement of fluid parameters,” which is issued in 2001. Theviscosity obtained by this way is not the viscosity in each individualbottle. The time-of-flight in that patent is measured in such a way thatthe transmitter and receiver or reflector are well aligned and theirdistance is fixed. These conditions, good alignment and fixed distance,are not available for a beverage bottle: curvature of bottle surfacedemands a strict alignment, perception of as small as 1% variation ofsound speed in beverages needs to on-line measure the real bottlediameter and wall thickness of each sample instead of using the nominalthickness.

SUMMARY OF THE INVENTION

Therefore, first object of the present invention is to provide acontainer inspecting apparatus and method which can on-line detect theFOs contained in bottles of materials of both low and high density, andboth transparent and opaque, with high inspection speed, safety and lowcost. Further object is to realize automatically on-line sorting orclassifying filled bottles based on their quality index, i.e., viscositycorrelated with ultrasound velocity measurement.

The present invention provides an apparatus for inspecting the foreignobjects packed in beverage bottles, comprising: a transporting means, anultrasonic transducer array disposed in the conveyor gap and underneaththe conveyor level, a linear water jet nozzle accommodating theultrasonic transducer array, a multi-channel pulse/receiver board toproduce and receive ultrasonic pulse signals, two ultrasonic transducersplaced separately on each side of conveyor, two round water jet nozzles,a two-channel pulse/echo board, and a computer to control themulti-channel pulse/receiver board and process the signals.

With the above arrangement, beverage bottles are transported onto thefirst conveyor after filling. The first conveyor moves forward thebottles to pass by the inspection gap where the ultrasonic transducerarray transmits an ultrasound pulse and receives echo signals. Theultrasound pulse is transmitted to the bottom of the bottle via waterjet coupling. The ultrasound transducer array is set on by apulse/receiver board controlled by a computer. Echo signals areprocessed by computer by examining both the time of flight and theamplitude of the pulse. Bottles are deviated out of the production lineif FOs are detected. Bottles without FOs continue moving forward andpassing by viscosity test station formed by two face-to-face placed oneach side of the conveyor. The ultrasound velocity in the beverage inthe bottle is accurately measured by the two transducers taking intoaccount of the bottle diameter and wall thickness. Viscosity of beverageinside the bottle is evaluated by correlation between the ultrasoundvelocity and the viscosity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is front and top views of a container inspecting and qualitysorting apparatus.

FIG. 2 is front and cross section views of water jet nozzle andultrasound transducer array.

FIG. 3A shows ultrasonic scanning on the bottle bottom with no foreignobject present. FIG. 3B shows ultrasonic scanning on the bottle bottomwith a foreign object present.

FIGS. 4A, 4B and 4C are schematics of ultrasonic echoes from outer andinner surfaces of glass bottle bottom in absence and presence of foreignobject.

FIG. 5 is a schematic of single ultrasonic transducer scanning a bottlebottom.

FIG. 6 shows ultrasonic signal propagation in the system of FIG. 5.

FIG. 7 is a zoomed picture for FIG. 6 around 42 μs, demonstratingoverlapped echoes from outer and inner surfaces of bottle bottom.

FIG. 8 is the center nominal frequency amplitude history calculated byusing short time Fourier transform for the signal shown in FIG. 7.

FIG. 9 is a scanning path of single ultrasonic transducer shown in FIG.5 for foreign object detection.

FIG. 10 is a tomograph of a glass fragment sediments on the bottom ofthe container scanned by the device as shown in FIG. 5.

FIG. 11 is the normalized spectrum of echo signal from outer surface ofPlexiglas plate of 4.40 mm thick. The frequency of the maximum amplitudeshifts to lower side as the incident angle increases.

FIG. 12 is the normalized spectrum of echo signal from outer surface ofglass plate of 2.67 mm thick. The frequency of the maximum amplitudeshifts to lower side as the incident angle increases.

FIGS. 13A and 13B illustrate a time history of center frequencyamplitude calculated by windowed short time Fourier transform for a realtime echo signal propagated in orange juice filled in a glass bottle.

FIG. 14 is the results of viscosities of juices and suspension as afunction of the ultrasound velocity.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, the beverage bottle inspection system includes twosubsystems. The first subsystem is the container foreign objectinspecting apparatus which comprises an ultrasound transducer array inconjunction with a linear water jet nozzle, two conveyors and thelateral barrier accordingly. The second subsystem consists of twotransducers, circular water jet nozzles and a two-channel pulse/echoboard with high speed mode switching.

The bottles 1 after filling are transported by conveyor belt 2 andwheels 4 to the flat stage 9. Bottles 1 on stage 9 are then pushed bybottles behind to pass by the gap between the two flat stages 9. Barrier5 is designed to keep the bottle straight-moving and prevent the bottlefrom falling down. Simultaneously, water is projected upward to thebottle bottom from the linear nozzle-house 10 sitting in the gap.Ultrasound pulse is produced by transducer array 11 and transmittedthrough water jet to the bottle bottom shown in FIG. 2. Array base 12 isused to support the array elements 10 and to transfer the echo signalsto pulse/receiver board piloted by a computer 13. The computer 13includes a processor, memory, hard drive and any other necessaryhardware to control and receive data from the transducer array 11 andtransducers 6 and 7. The computer 13 is suitably programmed to performthe data analysis described below.

Two echo signals respectively from outer and inner surfaces of thecontainer bottom are examined for their amplitudes which depend on theimpedances on the interface of two materials, i.e., water/bottom andbottom/beverage. These two echo signals are represented by P₁ and P₂respectively for outer and inner surfaces of the bottle bottom shown inFIG. 3.

In absence of FOs, the two reflections pressure ratio is calculated by:$\begin{matrix}{\frac{P_{2}}{P_{1}} = {\frac{4Z_{w}Z_{m}}{\left( {Z_{w} + Z_{m}} \right)} \cdot \frac{\left( {Z_{b} - Z_{m}} \right) \cdot {\mathbb{e}}^{{- \alpha}\; h}}{\left( {Z_{b} + Z_{m}} \right)\left( {Z_{m} - Z_{w}} \right)}}} & (1)\end{matrix}$where Z_(w), Z_(m), Z_(b) are respectively the acoustic impedance ofwater, container material, and the beverage. α and h are respectivelythe acoustic attenuation coefficient of the container material and thethickness of the container bottom.

The pressure ratio P₂/P₁ is changed in presence of foreign objects inthe container bottom due to the superimposition of the reflection of theforeign object to P₂ as shown in FIG. 4. The change of pressure ratioP₂/P₁ is used as criteria for inspecting FOs.

From a theoretical standpoint, the presence of FOs can be detected bymeasuring the pressure amplitude of the second reflection; given thatthe incident pressure P is shown in FIG. 3. However, the incidentpressure in many cases is unknown as it represents the pressure justbefore impacting the container. This pressure can be estimated based onthe pressure propagation from the transducer through the delay line, tothe nozzle, and finally to the outlet of the nozzle. This calculation isinaccurate due to signal attenuation, complexity of the geometry of thenozzle, instability of transducer driving voltage, and variations in thegap between the nozzle and the container bottom due to container surfaceirregularity. All these factors may lead to false FO detection. Incontrast, the pressure ratio between P₂ and P₁ is immune to such anomalysince the above variations vanish as a result of the division operation(P₁ and P₂ are both proportional to the incident pressure and aresubject to the same uncertainties).

It may also be noted that Equation (1) seems independent of frequency,as there is no explicit frequency terms in these equations. However,this is not the case. The frequency dependence comes from pressurevalues which are derived from the frequency spectrum of the reflections.In order to enhance the signal to noise ratio to obtain accurate signalpeak values from the spectrum an algorithm for signal selection andseparation is needed. Signal selection and separations is not an issueif the bottom is thick enough (time-of-flight of pulse in the containerbottom is much larger than the pulse duration).

One can readily separate two echoes signals and perform spectrumcalculation of each echo by augmenting the rest of the signal by zerosin this case. If the bottom is not thick enough, which may happen tomany practical applications, it is difficult to determine where toseparate the two close placed or even overlapped signals, because smallshift for separation point may lead to big difference in spectrumcalculation result. To overcome this problem an algorithm oftime-frequency analysis (windowed short time Fourier transform) wasdeveloped. In this algorithm a sliding window of width N was used tochop the sampled signal. A Fast Fourier Transform (FFT) was applied tothese N points to determine the amplitude of the pulse center frequency.The window was then moved forward one point along the signal to performthe same operation. Repeating this process throughout the signal, thehistory of the pulse amplitude at center frequency was obtained. The twoechoes appear as two separated peaks in the time history. In this methodit does not need to subjectively determine the separation point for thetwo narrowly spaced echoes. The only thing to do is to slide the windowand calculate the spectrum, which is especially suitable for computerprogramming.

The window width N was important for this technique. Large N has higherfrequency resolution but poor time localization and small N has reverseconsequence. In principle, the window width is so determined that 99%energy of the pulse is included. To minimize the impact of phase on thespectrum amplitude Hamming or Hanning rather than rectangular window isrecommended to be employed prior to the FFT operation.

After going through the FOs detection, the viscosity of beverage in eachbottle is evaluated passing by the viscosity test station. Theultrasound velocity C_(b) in the beverage is calculated by:$\begin{matrix}{c_{b} = {\left( {\frac{t}{t_{b}} - \frac{h_{1} + h_{2}}{c_{m}t_{b}} - \frac{L - h_{1} - h_{2}}{c_{w}t_{b}} - 1} \right) \cdot c_{w}}} & (2)\end{matrix}$where, as shown in FIG. 4, L is the distance between the twotransducers, c_(w) and C_(m) are sound velocities for water and thebottle material, h₁ and h₂ are thickness of the bottle wall closerespectively to transducers 6 and 7, t is the traveling time of pulsefrom transducer 6 to 7 when the bottle is situated in the pulse path,t_(b) is the traveling time of echoes between the two inner walls.

Sound velocity of the beverage C_(b) is measured in the followingprocedure. The two aligned transducers 6 and 7 are first set tothru-transmission mode to get the traveling time t when the bottle issituated in the ultrasound beam path between the two transducers. Thenthe two transducers are switched to pulse/echo mode to measure the timeof flight of echoes between the inner and outer surfaces of the bottlewalls close respectively to the two transducers. The thickness h₁ and h₂are equal to the sound velocity in the bottle material multipliedrespectively by the time of flight in each side. The ultrasoundpropagation time t_(b) in beverage in the bottle of inner diameter d isthe time difference between the second and third echoes obtained inpulse/echo mode.

A key technique in the sound velocity measurement in the above procedureis that the measurement should be performed when the bottle is wellaligned with the two transducers. For a circular cross section bottlethis means that the ultrasound beam emitted by the transducer is normalto the surface of the bottle. A simple way to detect if the bottle is ingood alignment with the two transducers is to check the amplitude of theecho from the outer surface of the bottle. When the bottle is wellaligned with two transducers, the echo amplitude of the outer surface ofthe bottle should be the maximum. This method was used to determine thenormal to the skin for automated meat grading by ultrasound sensors, andclaimed by A. A. Goldenberg, N. Kircanski, and Z. Lu in U.S. Pat. No.6,322,508, entitled “Automated meat grading method and apparatus” issuedin 2001. However, maximum-echo amplitude is not always a reliablecriteria for the normal searching. For example, the driving voltagefluctuation and the distance variation between the water jet nozzle andthe target can lead to an error determination in the normal searching.In the present invention, a frequency shift criteria is used to judgethe alignment of the bottle. In this method, the spectrum of the outersurface echo is calculated and the frequency of the maximum amplitude istherefore examined. For a given transducer the frequency of the maximumamplitude in the spectrum is called nominal center frequency andprovided by the manufacture, which is determined by an experimentorienting the transducer normal to the surface of the object. Thefrequency of the maximum amplitude in spectrum of the echo signal islower than the nominal frequency if the transducer is not normal to theobject surface. Since this criteria used in the present invention is thefrequency shift of the maximum amplitude instead of maximum amplitude inthe spectrum, this method is immune to uncertainties due to the drivingvoltage and distance changing produced amplitude fluctuation.

In the course of inspection, the transducer 6 is set to pulse/echo modeto continuously examine the frequency of maximum amplitude in thespectrum of outer surface echo. As soon as the center frequency of thetransducer is reached, the transducers 6 and 7 are first switch tothru-transmission mode to measure the traveling time t and then both topulse/echo mode to measure thickness h₁, h₂ and traveling time t_(b) asexplained in the above.

The following examples illustrate the principles applied to theinspection system of the present invention.

EXAMPLE 1

Bottom scanning for foreign object detection and tomograph.

The experimental set-up of the prototype is shown in FIG. 5. Apolystyrene container with flat bottom of thickness 0.75 mm wassupported by a holder. An ultrasonic transducer with delay line ismounted on the bottom of a plexiglass water jet nozzle that is suppliedwith water by a flow controllable pump. The delay line is made of aplexiglass cylinder of 7.40 mm in diameter and 10 mm in length thatproduces a time delay of 7.6 μs. The nozzle has a 3 mm diameter at exit.The ultrasound pulse is transmitted to the bottom of the polystyrenecontainer through the water jet. The ultrasound signal travelingdistance is 23.70 mm from the delay line to the exit of the nozzle. A 2mm gap is kept between the container bottom and the nozzle tip so thatthe transducer sitting on the x-y table can scan the container bottomsmoothly. The water flow is controlled at a rate of 40 liters per hour.

The transducer used was a flat-focused ultrasonic transducer of centerfrequency 4 MHz. The ultrasonic pulse was coupled to the water by delayline. A SR-9000 Pulse/Receiver card was used to drive the transducer andto receive the echo signal.

Pulses were produced by SR-9000 at a repetition rate of 2 kHz. Thesignal sampling frequency was 100 MHz.

Tap water was used for both the water jet and in the container. Fivespecimens: plexiglass, glass, aluminum stainless steel and copper, weretested. All these specimens were cut into pieces of 10 mm in squarewhose acoustic parameters are listed in Table 1.

A Labview 5.0 program was composed to control the SR-9000 card and thex-y table, and to process the echo signals simultaneously. The resultwas displayed on the monitor in real time.

TABLE 1 Acoustic impedance for materials used in experiment MaterialImpedance [kg/m²s] Polystyrene 2.47 × 10⁶ Plexiglass 3.16 × 10⁶ Glass12.3 × 10⁶ Aluminum   17 × 10⁶ Stainless steel 45.45 × 10⁶  Copper 41.61× 10⁶  Water 1.48 × 10⁶

FIG. 6 is a signal from the container without specimen presence. In thisfigure, the echo timing is shown from the interface of piezo/plexiglassdelay line to the interface of water jet/back face of container, where7.6 μs is the round trip time of ultrasound in the delay line, 32 μs isthat of water in the nozzle. The 32 μs delayed tip pulse is due to thediscontinuity of tip boundary. After the reflection on the interface ofdelay line/water, a pulse was observed which is the second reflection onthe same interface. Some noise before the container outer surfacereflection time could come from shear wave of the delay line. Thereflections from front and back faces are after the nozzle tip pulse,which happens at approximately after 42 μs.

FIG. 7 is the zoomed picture of two echoes from outer and inner surfaceof the bottom. It can be seen that the two echoes are overlapped anddifficult to separate for performing spectrum calculation for each echo.

FIG. 8 is the time history of the amplitude at center frequency of 4 MHzfor the signal of FIG. 7 by using the “slide window” technique. Thefirst peak is the amplitude of reflection of front face and the secondpeak is that of back face. The time difference between two reflectionsstays unchanged equal to that for the real time signal, but the peakswere easy to be sorted out and the pressure ratio P₂/P₁ is readilycalculated.

Table 2 is a summary of using pressure ratio method to detect foreignobjects of different materials. The results show that pressure ratioP₂/P₁ has significant changes from no-FO in presence of foreign object.This change heavily relies on the impedance difference: the bigger theimpedance difference between the FO and the container, the larger thepressure ratio difference.

TABLE 2 Experimental results and comparison with theoretical predictionsMaterial Measured P₂/P₁ No FO in container 0.91 ± 0.03 Plexiglass piecein container 1.23 ± 0.01 Glass piece in container 2.85 ± 0.03 Aluminumpiece in container 2.99 ± 0.08 Copper piece in container 3.29 ± 0.29Stainless steel piece in container 3.28 ± 0.07

Using the slide window method and the pressure ratio criterion, specimenof glass in the container was inspected. It was found that the specimencan be detected as small as 2.5×2.5 mm square which is smaller than thenozzle cross section area.

FIG. 9 is a schematic of FBs detection by using ultrasonic beam scanningwith x-y table. By this way the FBs' size can be estimated by directlyreading the distribution of reflections pressure ratio.

FIG. 10 is a pressure ratio distribution of a glass specimen of 2.5×2.5mm. The resolution of x-y table is 0.025 mm. The scale in the figure is0.25 mm per division. A matrix of 17×18 for pressure ratio is obtainedfor 17 line scanning with 18 measurement on each. Roughly the amplituderatio is larger when the transducer is right underneath the specimenthan far away from the specimen. The space between two peaks is 5divisions corresponding to 2.5 mm of the specimen size. However, themaximum amplitude did not occur in the center position. The reasons wasthat ultrasound beam was not perfectly perpendicular to the front faceat that moment due to loosening produced tilting of the nozzle in courseof x-y table movement. This phenomenon did not come out again afterfixing the nozzle. This phenomenon also indicates the importance of goodalignment in ultrasonic measurement.

SUMMARY

The above example shows that the foreign objects on the bottom ofcontainer can be detected and localized by the present inventionexamining the pressure ratio between the inner and outer surface of thebottom, which is immune to the instability of driving voltage and thedistance fluctuation between the transducer and the container bottom.Using of windowed short time Fourier transform can improve the speed ofecho signal recognition and are therefore suitable for rapid real timeinspection in production lines.

EXAMPLE 2

Automatic sensing for the bottle alignment using nominal centerfrequency shift principle: Using a transducer of nominal centerfrequency of 8.5 Mhz and the same pulse/receiver card as in example 1the nominal frequency was investigated by changing the incident angle ofthe transducer to the object being inspected. In this experiment, thetransducer/nozzle was mounted on a rotary stage of angular resolution0.16 degree. The experiment was started by orienting the nozzle at rightangle to object being inspected. Then the rotary stage was rotatedclockwisely and counterwisely to 2° with increment of 0.33°. Thereflected signals were sampled for every rotation of the stage. 100signals were sampled for each angle and averaged. The amplitudesspectrum were normalized by the maximum amplitude of each spectrum.Different amplitude of echo signals was obtained using Plexiglas andglass plate because their big difference in acoustic impedance. Theresult is presented in FIGS. 11 and 12 for spectrum of echoes fromPlexiglas and glass sample. The frequency of the maximum amplitude inthe spectrum shifts to lower side in both cases as the incident angleincreases. Although the reflection amplitude of glass is 2.4 timesgreater than that of the Plexiglas the normalized spectrum and thefrequency shift is identical for both samples.

By this method the frequency of maximum amplitude is confirmed as 8.5MHz for the given transducer at the right angle incident. The figuresalso show the high sensitivity of this method for the normal tracking ofa surface: the maximum amplitude frequency changes from 8.5 to 3 MHzwhen the incident angle varies from zero to two degree, which ispreferred for rapid alignment determination in production line.

EXAMPLE 3

Ultrasound velocity and viscosity measurement for bottled beverage andtheir correlations.

Using the auto localization technique described in example 2 and basedon equation (2) the ultrasound velocities in juices were measured.Juices were contained in a glass bottle of 41.63 mm nominal outerdiameter and 1.55 mm wall thickness. Orange juice without pulp, tomatojuice, and suspension of RC/CL were used in the tests. The RC/CL is aco-processed blend of cellulose gel (microcrystalline cellulose) andcellulose gum (sodium carboxymethyl cellulose), used as an ingredient infood processing. Beverages of various qualities were obtained by addingdilution water in juices.

FIG. 13 is the real time signal of orange juice sampled by transducer 6using pulse/echo mode and the time history of the amplitude at centerfrequency in spectrum obtained by using slide window. The thickness h₁is calculated by the time difference between the echoes from the outerand inner surfaces of the bottle shown in the figure. The thickness h₂is obtained by transducer 7 in the same way. Propagation time t_(b) inthe beverage is calculated by the difference between the two inner wallsurfaces, which are the second and the third peaks after the outersurface peak in FIG. 13.

Viscosities of beverages were measured at shear rate of 10.47 rad/s by aconcentric rotational viscometer. Diameters of the two cylinder arerespectively 56.20 and 103.20 mm. Samples' temperature was controlled towithin 20±0.28° C.

FIG. 14 shows the experimental results of viscosity and velocity ofsound measured for tomato and orange juices and RC/CL suspension. Theround, diamond and triangle points in the figure are experimental data.The velocity of sound in tomato juice is found in agreement in rangewith published data. See e.g., R. Saggin, and J. N. Couplant,“Concentration measurement by acoustic reflectance,” J Food Sci., vol.66, pp. 681–685 (2001). It was not found pertinent velocity data oforange juice for comparison with our experimental results. The solid anddashed lines in the figure are correlation between the viscosity μ andultrasound velocity C_(b), which is best represented by a quadraticrelation (3).μ=a ₂ c _(b) ² +a ₁ c _(b) +a ₀  (3)

Table 3 contains coefficients for Equation (3) for two juices withcoefficient (R²). It is demonstrated that the viscosity of beverages ishighly quadratically correlated with the velocity of sound. Thisrelationship can be used in the bottled beverages viscosity on-linetest. Correlation coefficients a₀, a₁, and a₂ are different depending onthe juice to be inspected.

TABLE 3 Coefficients for Equation (3) with coefficients (R²) ofdetermination a₂ a₁ a₀ R² Tomato Juice 10 × 10⁻⁶ −0.0422 31.552 0.9927Orange Juice 0.7 × 10⁻⁶  −0.0021 1.565 0.9732 RC/CL suspension 50 × 10⁻⁶−0.1553 115.52 0.9740

1. A system for aligning a wall with at least one device comprising: apulse producer for imparting a pulse signal on the wall; a pulsereceiver for receiving an echo signal from the wall; and a signalprocessor for analyzing a frequency of the echo signal to determinealignment of the wall relative to at least one of the pulse producer andthe pulse receiver.
 2. The system of claim 1 wherein the signalprocessor uses a center frequency shift principle to determine thealignment.
 3. The system of claim 1 wherein the signal processordetermines a frequency spectrum of the echo signal.
 4. The system ofclaim 3 wherein the signal processor determines a first frequency havinga maximum amplitude in the frequency spectrum and then determiningalignment based upon the first frequency.
 5. The system of claim 3wherein the signal processor determines alignment based upon acomparison of amplitudes of a plurality of frequencies in the frequencyspectrum.
 6. The system of claim 1 wherein the echo signal is areflection off the outer surface of the wall.
 7. A method fordetermining an orientation of a wall including the steps of: imparting apulse signal on the wall; receiving an echo signal from the wall;performing a frequency analysis of the echo signal; and determining anorientation of the wall relative to at least one of the pulse signal andthe echo signal with the wall based upon the frequency analysis.
 8. Themethod of claim 7 further including the step of using a center frequencyshift principle to determine the orientation.
 9. The method of claim 7further including the step of determining a frequency spectrum of theecho signal.
 10. The method of claim 9 further including the step ofdetermining a first frequency having a maximum amplitude in thefrequency spectrum and then determining alignment based upon the firstfrequency.
 11. The method of claim 9 further including the step ofdetermining orientation based upon a comparison of amplitudes of aplurality of frequencies in the frequency spectrum.
 12. The method ofclaim 7 wherein the echo signal is a reflection off an outer surface ofthe wall.
 13. An on-line system inspection of bottled beveragescomprising: a conveyor; a pulse producer proximate the conveyor forimparting a pulse signal on a wall of a bottle transported on theconveyor, a pulse receiver proximate the conveyor for receiving an echosignal from the wall; and a signal processor for analyzing a frequencyof the echo signal to determine alignment of the wall relative to atleast one of the pulse producer and the pulse receiver as the conveyorcarries the bottle.
 14. The system of claim 13 wherein the signalprocessor uses a center frequency shift principle to determine thealignment.
 15. The system of claim 13 wherein the signal processordetermines a frequency spectrum of the echo signal.
 16. The system ofclaim 15 wherein the signal processor determines a first frequencyhaving a maximum amplitude in the frequency spectrum and thendetermining alignment based upon the first frequency.
 17. The system ofclaim 15 wherein the signal processor determines alignment based upon acomparison of amplitudes of a plurality of frequencies in the frequencyspectrum.
 18. The system of claim 13 wherein the echo signal is areflection off an outer surface of the wall.
 19. The system of claim 13wherein the signal processor analyzes a frequency spectrum of the echosignal, identifies a first frequency having the maximum amplitude in thefrequency spectrum and compares the first frequency to a nominalfrequency, the signal processor determining whether the bottle isaligned based upon the comparison of the first frequency to the nominalfrequency.